1. Field of the Invention
The present invention relates to a bent pipe, more particularly a bent pipe having an inner diameter less than a medium dimension, having a fused abrasion resistance layer on its inner surface formed by a thermal spraying and fusing of a self fluxing alloy. The bent pipe according to the present invention may be preferably used in a pipeline for delivering synthetic resin pellets.
2. Background of the Art
Various methods have been conventionally taken for improving the abrasion resistance of the bent pipe used in a pipeline for transporting granulates or slurries.
One of such methods is known as a method that an abrasion resistance metal is padded by welding on the inner surface of the bent pipe to form an abrasion resistance layer. While this method may however be relatively easily applied to the inner surface of the bent pipe having a larger diameter, it is impossible to pad it on the inner surface of the bent pipe having a medium or small diameter of 15 cm and less. In case of the bent pipe of medium or small diameter, there is another method for making a padding easy, showing FIG. 4. According to the method, a pipe 1 is cut in the direction to the center of a circle of the curvature of the bent pipe to be separated into a plurality of partitioned portions (22, 23 . . . ), followed by that an abrasion resistance metal is padded by welding on the inner surface of each of the separated parts before they are welded with the cut surfaces met together for integration. This method results in forming welded zones on the inner surface of the outer bent pipe portion. The obtained padded layer of the abrasion resistance metal may sometimes be integrated insufficiently or occur an undesired roughness. Also, the articles passing through the bent pipe may hit most intensely against the outer bent portion among the inner surfaces of the pipe body. Thus, when the welded zone is formed at the outer bent portion, from which an abrasion tends to be progressed so that the life of the bent pipe can not be sufficiently prolonged. Also, the bent pipe having an increased number of portions to be welded involves a trade off in the cost of preparing.
On the other hand, there is also known as a method illustrated in FIG. 5 wherein the pipe body 1 is cut along a curved face that includes the central axis and that is perpendicular to a plane including its central axis so as to be separated into two partitioned portions followed by that an abrasion resistance metal is padded by welding at the inner surfaces of these partitioned portions before each of the separated portions is met for welding together with their cut surfaces associated so as to obtain a unification. This method however has a drawback that since the pipe body is largely deformed in padding the abrasion resistance metal, an operation may be required for approximating the deformed body to the original shape. Further, since the end portions will not assume completely round sections, it is difficult to attach flanges to the end portions.
Another method is also known that the pipe body is partitioned at a plane including the central axis of the pipe body. This method is accompanied by forming a welded zone at an outer bent portion of the inner surface of the bent pipe, by which the obtained bent pipe can not provide a sufficiently prolonged life.
Further, there is a method that a padding layer of hard metal 25 is formed at an outer surface of the bent pipe body 1 followed by that the padding layer of hard metal 25 is covered with a coating layer of reinforced plastic, illustrated in FIG. 6, which is disclosed in Japanese Patent Publication No. 62-4598 (1987). This method may not accompany any problems relating to a welded zone since the pipe body is not cut, but accompany another problem that the bent pipe may abrade to intermingle the transported article with impurities since the bent pipe having an uncoated inner surface has a lower hardness, which sometimes contaminate the passing articles. Also, this method requires complicated treatment for covering the outer surface of the bent pipe with a reinforced plastic layer.
Therefore, there is an object to provide an improved technique for preparing a bent pipe with a proper abrasion resistance layer.
There is provided a bent pipe and a method thereof. This bent pipe is provided with a pipe body consisting of an outer bent portion and an inner bent portion. The pipe body has an inlet hole on one end of the pipe body, an outlet hole on the other end of the pipe body, and an inner surface extending to communicate the inlet hole with the outlet hole. The pipe body is then cut along a curved face. The curved face is perpendicular to a plane including a central axis of the pipe body and that extends not to cross the inlet hole and the outlet hole but to include a part of the central axis. Therefore, the pipe body is divided into a first partitioned part having at least one of the groups of the inlet hole and the outlet hole, and a second partitioned part. A self fluxing alloy is sprayed by thermal spraying and fused so as to form a fused abrasion resistance layer on the inner surface of at least the outer bent portion of the pipe body. Thereafter, the first partitioned part is fitted into the second partitioned part for welding to obtain a present bent pipe.
The first partitioned part may also include the outer bent portion having both of the inlet hole and the outlet hole.
Further, the fused abrasion resistance layer may preferably be formed on an edge of at least the inlet hole among the inlet hole and outlet hole.
The present invention is further clarified to those skills in the art by referring to the following description and appended drawings.